Arriving with few new content deals despite months of heavy hype, the half-inch thick gadget, which looks like a giant iPhone, met with mixed reviews.

But Apple’s co-founder and chief executive called it a “revolutionary product” that would fill the gap between smartphones and laptop computers.

Mr Jobs said the iPad would have a wide range of uses, from e-mailing and internet browsing to viewing videos and reading e-books.

“If there’s going to be a third category it has to be better at these tasks, otherwise it has no reason for being,” said Mr Jobs. The Apple chief is still looking thin after a fight with cancer.

Challenging the big mobile technology companies, Mr Jobs said Apple’s total revenues from mobile gear – including its iPod and iPhone lines – now exceeded those of Nokia. “We’re a mobile company. That’s what we do,” he said.

“It’s clearly not a game-changer, [like] the iPhone,” said Ashok Kumar, analyst at Northeast. “The killer application is missing.”

The new iBooks store and electronic reading functions “stand on the shoulders” of Amazon’s Kindle, Mr Jobs said, offering titles from a handful of publishers to start, including HarperCollins and Penguin.

Apple said the iPad would start shipping in the US in 60 days, with a price of $499 for a bottom-of-the-range model. The top version, with the ability to connect to AT&T’s 3G network, will sell for $829.